1. Field of the Invention
This invention relates to integrated circuits and, more specifically, to ESD protection for integrated circuits.
2. Brief Description of the Prior Art
Electrostatic discharge (ESD) may cause damage to semiconductor devices in an integrated circuit during handling of the integrated circuit chip package, this being particularly true in the case of MOS circuitry including DRAMs. It is therefore necessary to protect such circuits against damage due to stress conditions such as high energy, high voltage and/or high current pulses. Prevention of such damage generally is provided by protection circuits incorporated into the chip of the integrated circuit. In general, such protection circuits present high impedance or an open circuit therefrom during normal operating conditions of the integrated circuit and switch to low impedance under the above described stress conditions. Such protection circuits generally include a switch which is capable of conducting relatively large currents during an ESD event. Various devices such as silicon controlled rectifiers (SCRs), which are PNPN-type devices, can be and have been utilized to provide the switching function required to essentially shunt the protected circuitry during an ESD event and such prior art devices and a standard manner of fabrication thereof is set forth in the above noted Ser. No. 08/302,145.
Prior art circuits and structures used for ESD protection can withstand high levels of ESD stress. However, recent advances in technology have produced devices with increasingly smaller geometry. This smaller geometry results in devices which can fail at voltage levels lower than the triggering voltages of prior art protection circuits. Accordingly, improved ESD protection has been sought, one such ESD protection circuit being set forth in the above noted application Ser. No. 08/302,145.